Environmentalists say that highlights the continuing threat that invasive fish will reach the Great Lakes.

The U.S. Fish and Wildlife Service released data this week from 228 water samples collected in October. Twenty-three tested positive for DNA from silver carp, one of several Asian carp species that infest many Midwestern rivers.

Silver carp are notorious for springing from the water and sometimes colliding forcefully with boaters.

Just one live Asian carp has been found in the Chicago waters, but their DNA has turned up repeatedly in samples. The Alliance for the Great Lakes says some of the recently detected DNA was found less than a city block from Lake Michigan.